The present invention relates to write driver circuitry for a magnetic data storage device, and in particular to a voltage-type write driver circuit for use with a transmission-line interconnect.
Magnetic data storage devices, and in particular hard disk drive storage devices, have become an essential component in modem computer systems. An example of a well-known hard disk drive storage device 100 is shown in FIG. 1. Hard disk drive 100 includes an enclosure 101, which contains one or more magnetic media platters or disks 102, read elements 104, write elements 105, an actuator arm suspension 106, a transmission line (T/L) interconnect 108, a read/write integrated circuit 110, a flexible interconnect cable 112, and a disk enclosure connector 114. Magnetic media disks 102 store information on their surfaces. Read elements 104 and write elements 105 are mounted on actuator arm suspension 106 and are located in proximity to the surfaces of disks 102. Actuator arm suspension 106 moves transducers 104 into proximity to a selected portion of disks 102 which contains the information to be read, or which will contain the information to be recorded. Write elements 105 write information in response to input electrical signals, and read elements 104 read recorded information and output electrical signals representing the information.
The electrical signals are communicated between read/write transducers 104 and read/write integrated circuit 110 over T/L interconnect 108. Read/write integrated circuit conditions the electrical signals so that they can drive write element 105 during writing and amplifies the electrical signal from read element 104 during reading. Signals are communicated between read/write integrated circuit 110 and disk enclosure connector 114 over flexible cable 112. Disk enclosure connector 114 conducts signals with circuitry external to disk enclosure 101.
A profile view of the structure of hard disk drive 100 may be in FIG. 2. Disk 102 include two disks, 102A-B, and there are four read elements 104A-D and four write elements 105A-D. Read/write integrated circuit 110 selects one of the read or write elements, after which data can be read from or written to the selected element, as appropriate.
When comparing the spectral content of the read and write signals, the write signals have higher frequency components than the read signals due to the square wave nature of the write voltage/current signals. To achieve high-data rates, the write system must therefore employ high-frequency interconnection techniques between the read/write integrated circuit and the write elements.
In a typical hard disk drive storage system, the read/write integrated circuit is located relatively far away (approximately 5 cm) from the write and read elements. Due to the length of the T/L interconnect, it is difficult to obtain the desired performance during writing of information to the disk. The performance of the transmission line interconnect and system may be enhanced by implementing the designs disclosed in U.S. Pat. No. 5,608,591. However, problems still remain with the design of a voltage-type write driver circuit that will provide the desired performance.
The present invention is a recording channel front-end circuit for driving a write element over a transmission line interconnect that will provide the desired performance during writing of information. In one embodiment, the recording channel front-end circuit includes a voltage-type write driver coupled to the transmission line interconnect and operable to output a write driver signal to the transmission line interconnect and a receiver termination circuit coupling the transmission line interconnect to the write element. The receiver termination circuit may include an impedance matching network operable match a terminal impedance of the write element to a characteristic impedance of the transmission line interconnect.
In another embodiment, the recording channel front-end circuit includes a voltage-type write driver coupled to the transmission line interconnect and operable to output a write driver signal to the transmission line interconnect and a source termination circuit coupling the voltage-type write driver to the transmission line interconnect. The source termination circuit may include an impedance matching circuit operable match a terminal impedance of the voltage-type write driver to a characteristic impedance of the transmission line interconnect.
In one aspect of the present invention the voltage-type write driver may include a voltage reference circuit operable to output a selectable voltage and an output driver operable output voltage driving signals representing write data signal transitions, the output voltage driving signals having an amplitude depending on the selected voltage output from the voltage reference source. The voltage-type write driver may further include a write gate circuit operable to enable the voltage-type write driver when in a write mode operation and disable the voltage-type write driver when not in a write mode operation. The voltage-type write driver may further include an output driver circuit comprising field effect transistors. The voltage-type write driver may further include an output driver circuit comprising bipolar transistors and the voltage reference circuit is further operable to output a selectable voltage including a diode offset voltage. The voltage-type write driver may further include a digital select interface coupled to the voltage reference circuit operable to receive digital signals indicated a selected voltage and to control the voltage reference circuit so as to output the selected voltage.
In another aspect of the present invention, the output driver circuit may include an output driver circuit having two outputs, each output operable to output a signal having two levels, a first level being dependent on a reference voltage. The output driver may further include a pair of inverter circuits, each inverter circuit operable to drive one of the two outputs, the inverter circuits operable to drive a first output with the first level and a second output with a second level or the first output with the second level and the second output with the first level. Each inverter circuit may include field effect transistors or each inverter circuit may include bipolar transistors. If the inverter circuit includes bipolar transistors, the inverter circuit may include a voltage clamping circuit.
The present invention is advantageous when used in a magnetic data storage device.